Messenger RNA (mRNA) directs protein synthesis. Antisense methodology is the complementary hybridization of relatively short oligonucleotides to mRNA or DNA such that the normal, essential functions of these intracellular nucleic acids are disrupted. Hybridization is the sequence-specific hydrogen bonding via Watson-Crick base pairs of oligonucleotides to RNA or single-stranded DNA. Such base pairs are said to be complementary to one another.
The naturally occurring events that provide the disruption of the nucleic acid function, discussed by Cohen in Oligonucleotides: Antisense Inhibitors of Gene Expression, CRC Press, Inc., Boca Raton, Fla. (1989) are thought to be of two types. The first, hybridization arrest, denotes the terminating event in which the oligonucleotide inhibitor binds to the target nucleic acid and thus prevents, by simple steric hindrance, the binding of essential proteins, most often ribosomes, to the nucleic acid. Methyl phosphonate oligonucleotides (Miller, et al., Anti-Cancer Drug Design 1987, 2, 117) and .alpha.-anomer oligonucleotides are the two most extensively studied antisense agents which are thought to disrupt nucleic acid function by hybridization arrest.
The second type of terminating event for antisense oligonucleotides involves the enzymatic cleavage of the targeted RNA by intracellular RNase H. A 2'-deoxyribofuranosyl oligonucleotide or oligonucleotide analog hybridizes with the targeted RNA and this duplex activates the RNase H enzyme to cleave the RNA strand, thus destroying the normal function of the RNA. Phosphorothioate oligonucleotides are the most prominent example of an antisense agent that operates by this type of antisense terminating event.
Considerable research is being directed to the application of oligonucleotides and oligonucleotide analogs as antisense agents for diagnostics, research reagents and therapeutic compounds. As research reagents oligonucleotides and oligonucleotide analogs find various uses including, but not limited to, probes and primers. For diagnostics, oligonucleotides and oligonucleotide analogs can be used in cell free systems, in vitro, ex vivo or in vivo. Currently a number of oligonucleotide based drugs are being tested in human clinical trials for various disease states including AIDS, against various cancers and for various systemic disease resulting from inappropriate immune responses. The antisense oligonucleotides and oligonucleotide analogs can be functionalized with various conjugate groups to modify certain of their properties. Thus reporter groups can be conjugated to the oligonucleotides or oligonucleotide analogs to assist in identification and location of the compounds in various testing medium including reagents, cellular products or digests, cell systems and organisms. Other conjugate groups can be utilized for transport, binding and uptake modulation, modification of solubility characteristics, analytical instrument identification and response and other useful properties known in the art.
Ramirez, et al., J. Am. Chem. Soc. 1982, 104, 5483, introduced the phospholipid group 5'-O-(1,2-di-O-myristoyl-sn-glycero-3-phosphoryl) into the dimer TpT independently at the 3' and 5' positions. Subsequently Shea, et al., Nuc. Acids Res. 1990, 18, 3777, disclosed oligonucleotides having a 1,2-di-O-hexyldecyl-rac-glycerol group linked to a 5'-phosphate on the 5'-terminus of the oligonucleotide. Certain of the Shea, et. al. authors also disclosed these and other compounds in patent application PCT/US90/01002. A further glucosyl phospholipid was disclosed by Guerra, et al., Tetrahedron Letters 1987, 28, 3581.
In other work, a cholesteryl group was attached to the inter-nucleotide linkage between the first and second nucleotides (from the 3' terminus) of an oligonucleotide. This work is disclosed in U.S. Pat. No. 4,958,013 and further by Letsinger, et al., Proc. Natl. Acad. Sci. USA 1989, 86, 6553. The aromatic intercalating agent anthraquinone was attached to the 2' position of a sugar fragment of an oligonucleotide as reported by Yamana, et al., Bioconjugate Chem. 1990, 1, 319. The same researchers placed pyrene-1-methyl at the 2' position of a sugar (Yamana et. al., Tetrahedron Lett. 1991, 32, 6347).
Lemairte, et al., Proc. Natl. Acad. Sci. USA 1986, 84, 648; and Leonetti, et al., Bioconjugate Chem. 1990, 1, 149. The 3' terminus of the oligonucleotides each include a 3'-terminal ribose sugar moiety. The poly(L-lysine) was linked to the oligonucleotide via periodate oxidation of this terminal ribose followed by reduction and coupling through a N-morpholine ring. Oligonucleotide-poly(L-lysine) conjugates are described in European Patent application 87109348.0. In this instance the lysine residue was coupled to a 5' or 3' phosphate of the 5' or 3' terminal nucleotide of the oligonucleotide. A disulfide linkage has also been utilized at the 3' terminus of an oligonucleotide to link a peptide to the oligonucleotide as is described by Corey, et al., Science 1987, 238, 1401; Zuckermann, et al., J. Am. Chem. Soc. 1988, 110, 1614; and Corey, et al., J. Am. Chem. Soc. 1989, 111, 8524.
Nelson, et al., Nuc. Acids Res. 1989, 17, 7187 describe a linking reagent for attaching biotin to the 3'-terminus of an oligonucleotide. This reagent, N-Fmoc-O-DMT-3-amino-1,2-propanediol is now commercially available from Clontech Laboratories (Palo Alto, Calif.) under the name 3'-Amine on. It is also commercially available under the name 3'-Amino-Modifier reagent from Glen Research Corporation (Sterling, Va.). This reagent was also utilized to link a peptide to an oligonucleotide as reported by Judy, et al., Tetrahedron Letters 1991, 32, 879. A similar commercial reagent (actually a series of such linkers having various lengths of polymethylene connectors) for linking to the 5'-terminus of an oligonucleotide is 5'-Amino-Modifier C6. These reagents are available from Glen Research Corporation (Sterling, Va.). These compounds or similar ones were utilized by Krieg, et al., Antisense Research and Development 1991, 1, 161 to link fluorescein to the 5'-terminus of an oligonucleotide. Other compounds of interest have also been linked to the 3'-terminus of an oligonucleotide. Asseline, et al., Proc. Natl. Acad. Sci. USA 1984, 81, 3297 described linking acridine on the 3'-terminal phosphate group of an poly (Tp) oligonucleotide via a polymethylene linkage. Haralambidis, et al., Tetrahedron Letters 1987, 28, 5199 report building a peptide on a solid state support and then linking an oligonucleotide to that peptide via the 3' hydroxyl group of the 3' terminal nucleotide of the oligonucleotide. Chollet, Nucleosides & Nucleotides 1990, 9, 957 attached an Aminolink 2 (Applied Biosystems, Foster City, Calif.) to the 5' terminal phosphate of an oligonucleotide. They then used the bifunctional linking group SMPB (Pierce Chemical Co., Rockford, Ill.) to link an interleukin protein to the oligonucleotide.
An EDTA iron complex has been linked to the 5 position of a pyrimidine nucleoside as reported by Dreyer, et al., Proc. Natl. Acad. Sci. USA 1985, 82, 968. Fluorescein has been linked to an oligonucleotide in the same manner as reported by Haralambidis, et al., Nucleic Acid Research 1987, 15, 4857 and biotin in the same manner as described in PCT application PCT/US/02198. Fluorescein, biotin and pyrene were also linked in the same manner as reported by Telser, et al., J. Am. Chem. Soc. 1989, 111, 6966. A commercial reagent, Amino-Modifier-dT, from Glen Research Corporation (Sterling, Va.) can be utilized to introduce pyrimidine nucleotides bearing similar linking groups into oligonucleotides.
Carbamate linkages have been utilized to link conjugate groups to oligonucleotides at the 5' position as reported by DeVos, et al., Nucleosides Nucleotides, 9, 259, 1990, Wachter, et al., Nucleic Acids Res., 14, 7985, 1986, and Gottikh, et. al., Tetrahedron Lett., 31, 6657, 1990. Carbamate linkages have not been used for link conjugate groups to the 2' nor the 3' position of nucleosides, however, carbamate linkages have been used to form fixed length 3' to 5' internucleoside linkage as reported by Stirchak et al., J. Org. Chem., 52, 4202, 1987.
While currently utilized nucleosides, nucleotides and oligonucleotides conjugate linking moieties certainly have great utility, there is a continuing need for improved conjugate linking groups have a potpourri of different properties. One such property is as a transitory blocking group during oligonucleotide synthesis. A further property is to provide a foundation at the 2' and 3' positions where "spacer" molecules of various lengths, e.g., diaminoalkyl groups such as 1,2-ethylene diamine and 1,6-diaminohexane, can be attached for modifying the spacing between the nucleosides, nucleotides or oligonucleotides and the conjugate group.